This invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit which is capable of converting a single 5 volt reference voltage to a high positive rail voltage (of the order of 25 volts or more) and/or a low negative rail voltage (of the order of -25 volts or less) for use in, for example, integrated circuits.
It is well-known that many integrated circuits require for their operation, in addition to a low primary voltage (e.g. of voltage +5 volts), multiple high positive and/or low negative rail voltages. Specifically, nonvolatile semiconductor memory devices such as an electrically erasable programmable read-only memory (E.sup.2 PROM) and non-volatile random access memory (NV RAM) typically require a 5 volt primary voltage for read access purposes and a .+-.25 volt rail voltages for programming (i.e. write and store, respectively) purposes. Hitherto, these voltage requirements have been met by means of multiple power supplies, one power supply for providing each of the required voltages. However, use of such multiple power supplies is disadvantageous not only from a cost standpoint but also since it necessitates insuring that each power supply satisfies the devices' stipulated operational limits. It is preferable that a nonvolatile memory device have a built-in or on-chip power supply that is capable of functioning by means of a single +5 volt power supply and generating the necessary high positive and low negative rail voltages for operation of the device.
One prior art technique of generating high positive and low negative voltages from a low voltage (+5 volt) source is by means of discrete transformer and series regulator circuits coupled to the low voltage source. However, due to their bulkiness, such transformer circuits are not suitable for integration on a chip. It may be possible to locate the transformer elements on a pc board and integrate the remainder of the circuit at the chip level. However, the transformers not only occupy a large area of the pc board but require manual insertion on the pc board which is not cost-effective. Another disadvantage of the transformer and series regulator circuits is that they generally dissipate a significant amount of energy, thereby rendering the circuit inefficient.
It is therefore an object of the present invention to provide an efficient solid-state switching power supply circuit which by utilizing a single +5 volt power supply is capable of generating rail voltages of up to .+-.25 volts.
Another object of this invention is to provide a switching power supply circuit that is conducive for integration on a chip except for a pair of inductors and a pair of capacitors which are relatively small in size (each element occupying approximately one square cm. area) and suitable for automated insertion on a pc board.
It is another object of this invention to provide a switching power supply circuit that utilizes a single pulse generator to drive both positive and negative rails, thereby minimizing the number of components (and therefore, chip real estate) required for the circuit.
These and other objects of the invention will be apparent from the following description.